water Article SHETRAN and HEC HMS Model Evaluation for Runoff and Soil Moisture Simulation in the JiˇcinkaRiver Catchment (Czech Republic) Vesna Ðuki´c* and Ranka Eri´c Faculty of Forestry, Department of Ecological Engineering for Soil and Water Resources, Protection University of Belgrade, Kneza VIšeslava 1, 11000 Belgrade, Serbia; [email protected] * Correspondence: [email protected]; Tel.: +381-60-367-4549 Abstract: Due to the improvement of computation power, in recent decades considerable progress has been made in the development of complex hydrological models. On the other hand, simple conceptual models have also been advanced. Previous studies on rainfall–runoff models have shown that model performance depends very much on the model structure. The purpose of this study is to determine whether the use of a complex hydrological model leads to more accurate results or not and to analyze whether some model structures are more efficient than others. Different configurations of the two models of different complexity, the Système Hydrologique Européen TRANsport (SHETRAN) and Hydrologic Modeling System (HEC-HMS), were compared and evaluated in simulating flash flood runoff for the small (75.9 km2) JiˇcinkaRiver catchment in the Czech Republic. The two models were compared with respect to runoff simulations at the catchment outlet and soil moisture simulations within the catchment. The results indicate that the more complex SHETRAN model outperforms Citation: Ðuki´c,V.; Eri´c,R. the simpler HEC HMS model in case of runoff, but not for soil moisture. It can be concluded that SHETRAN and HEC HMS Model the models with higher complexity do not necessarily provide better model performance, and that Evaluation for Runoff and Soil the reliability of hydrological model simulations can vary depending on the hydrological variable Moisture Simulation in the Jiˇcinka under consideration. River Catchment (Czech Republic). Water 2021, 13, 872. https://doi.org/ Keywords: hydrological models comparison; runoff calibration and validation; soil moisture valida- 10.3390/w13060872 tion; model structure; downscaled satellite soil moisture Academic Editors: Yves Coquet, Isabelle Cousin and Laurent Lassabatere 1. Introduction Floods and especially flash floods can have devastating consequences on the economy, Received: 7 February 2021 environment and people. It was found that large floods have occurred more frequently in Accepted: 16 March 2021 Published: 23 March 2021 recent years than in the past due to global warming [1]. Due to global warming, the Czech Republic was facing severe and destructive flooding in recent years. The hilly and torrential 2 Publisher’s Note: MDPI stays neutral JiˇcinkaRiver basin (75.9 km ) in the Moravian-Silesian region in the Czech Republic is with regard to jurisdictional claims in particularly affected by serious flooding due to steep slopes of the terrain, and a high published maps and institutional affil- percentage of types of soils with low-intensity infiltration [1]. iations. Hydrological models are important and necessary tools for flood and environmental resources management. In recent decades, due to rapid advances in computation power, considerable progress has been made in the development of complex hydrological models. On the other hand, simple conceptual models have also been advanced. The complex physically based and distributed models are a very useful tool as they can describe hy- Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. drological processes in great detail by taking into account different involved processes. This article is an open access article Due to their distributed nature, they can provide detailed information about the spatial distributed under the terms and variability of different components of the hydrological cycle within the catchment. The high conditions of the Creative Commons number of parameters incorporated in some rainfall–runoff models and the existence of Attribution (CC BY) license (https:// different sets of parameters producing similar model performance can increase the model creativecommons.org/licenses/by/ uncertainty and decrease the performance of the model. The problem of overparameteriza- 4.0/). tion in complex rainfall–runoff models has been addressed by many authors over several Water 2021, 13, 872. https://doi.org/10.3390/w13060872 https://www.mdpi.com/journal/water Water 2021, 13, 872 2 of 26 decades [2–5]. Compared to the distributed hydrological models, the benefits of lumped and semi-distributed models are fast computational time and the ability to use fewer data and fewer parameters than a distributed model while causing fewer problems of parameter uncertainty and over-parameterisation than more complex models [6–10]. Various studies have been conducted using model inter-comparison experiments in the field of streamflow simulation [7,8,10–21]. Through the inter-comparison of lumped conceptual models with a physical-based semi-distributed model, Tegegne et al. [15] concluded that the use of a more complex model could not be justified in data-poor catchments. Better performance of a lumped model over a semi-distributed model was also confirmed by Srivastava et al. [13] and Vansteenkiste et al. [17]. The reason for that Vansteenkiste et al. [17] found in the fact that the lumped models could be calibrated more accurately because they contain a smaller number of parameters and a much smaller computational time. Perrin et al. [19] and Grimaldi et al. [20] explored the role of complexity in hydrological models and analyzed the performances of different models with a different number of optimized parameters. They stated that the model performance depends very much on the structure of the model and that the model structure is the main reason why complex models lack their stability. The importance of selecting the optimal spatial discretization of watersheds for the development of reliable rainfall–runoff models was emphasized in many studies [21,22]. There are a number of studies in which different hydrological models have been used to investigate the effects of different watershed subdivisions on hydrologic model outputs. These studies include the semi-distributed conceptual models such as: the Soil and Water Assessment Tool (SWAT) model [23–25], the Hydrologic Modeling System (HEC-HMS) [21,22,26,27], the HBV, PREVAH, SWBM models [28,29] and the physically based and distributed CASC2D [30]. However, the results obtained in these studies are not consistent and may differ from one study to another. The purpose of this study is to determine whether the use of a complex hydrological model leads to more accurate results or not in the case of mountainous and flash flood catchments. An important way for better model comparison and for improving model parameterization is to collect and incorporate new and possibly more accurate data besides that of runoff (e.g., representing the internal states of the model) [31–37]. However, it can be seen that there are many more papers in which model comparisons and evaluations were performed only in respect of streamflow simulations [7,10–22]. In this study, two models of different complexity, the physically based and distributed the Système Hydrologique Européen TRANsport (SHETRAN) and the lumped and the semi-distributed variants of the HEC-HMS model, were compared and evaluated in simulating flash flood runoff at the catchment outlet and soil moisture simulations representing the internal behaviour of the catchment for the small (75.9 km2) JiˇcinkaRiver catchment in the Czech Republic. The SHETRAN rainfall–runoff model for the JiˇcinkaRiver catchment was established and presented in Ðuki´cet al. [31]. In this paper, different configurations of catchment spatial discretization were compared by applying the SHETRAN and HEC HMS model for the purpose of analyzing whether some structures are more efficient than others and how the model complexity affects the model performance. Although ground measurements provide the most accurate estimates of soil moisture, they are costly and provide only point-based measurements rather than areal data [38]. Remotely sensed soil moisture data covering wider areas present an alternative way for reaching information about the spatial and temporal dynamics of soil moisture within the basins. Good agreement between the values of soil moisture simulated by the application of hydrological models and satellite derived estimates of soil moisture was obtained for large basins [35,36,38–40]. The remotely sensed soil moisture data are used in this study to increase knowledge about the hydrological processes and to improve streamflow model estimates. However, due to relatively coarse spatial resolution of approximately several tens of kilometers, the remotely sensed data products cannot be effectively applied to hydrological studies in small catchments. The coarse resolution of the remotely sensed data products is inadequate to describe the high spatio-temporal variability of soil moisture in Water 2021, 13, 872 3 of 26 small catchments. Hence, over the past decades, various downscaling methods have been studied and used to improve the spatial resolution of satellite soil moisture products [31]. Usually, downscaled remotely sensed soil moisture products are validated against ground- based soil moisture observations and good agreement was found between them [41–43]. Thanks to this agreement, opportunities for a wider application of remotely sensed data in small catchments are provided. In that way,